We are trying to create a remake of the Diamond Dogs "The Black Hole" for our film course, and are trying to learn how to accomplish the effect of the actor's arm moving through the printed black hole...there are cases where it may just be camera trickery (like where the paper rests on the printer shelf and the viewer only sees that platform), but then there are such scenes where the actor holds up the paper and puts his arm through, both sides of the paper are visible yet his arm does not emerge out the other end.
If you haven't seen the short film (3min) here's the link:http://www.youtube.com/watch?v=P5_Msrdg3Hk
does anyone have an idea as to how this might be done?
Here is a general description of doing the rudimentary version of this:
Shoot the background without the foreground subject (the actor). This piece of footage is your "clean plate". Then shoot with the foreground element. Overlay the layer that includes the foreground element over the clean-plate layer. Then use a mask to cut out whatever part of the foreground layer you don't want to see---such as the actor's hand.
There's more to this, such as feathering the mask and such, but that is the very basic approach.
Since you're new to After Effects, I strongly recommend that you start here: